Methods for cleaving a bonded wafer structure

ABSTRACT

Apparatus and methods for mechanically cleaving a bonded wafer structure are disclosed. The apparatus and methods involve clamps that grip the bonded wafer structure and are actuated to cause the bonded structure to cleave.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit of U.S. ProvisionalApplication No. 61/553,447 filed Oct. 31, 2011, which is incorporatedherein by reference in its entirety.

FIELD OF THE DISCLOSURE

This disclosure generally relates to apparatus and methods for cleavinga bonded wafer structure and, more particularly, to apparatus andmethods that involve clamps that are actuated to cause the bondedstructure to cleave.

BACKGROUND

Semiconductor wafers are generally prepared from a single crystal ingot(e.g., a silicon ingot) which is sliced into wafers. The wafers areground and/or polished to produce product wafers. While reference willbe made herein to semiconductor wafers constructed from silicon, othermaterials may be used as well, such as germanium or gallium arsenide.

One type of wafer is a silicon-on-insulator (SOI) wafer. An SOI waferincludes a thin layer of silicon atop an insulating layer (e.g., anoxide layer), which is in turn disposed on a silicon substrate.

An exemplary process of making an SOI wafer includes depositing a layerof oxide on a polished front surface of a donor wafer and/or a handlewafer. Particles (e.g., hydrogen atoms or a combination of hydrogen andhelium atoms) are implanted at a specified depth beneath the frontsurface of the donor wafer. The implanted particles form a cleave planein the donor wafer at the specified depth at which they were implanted.The surface of the donor wafer is cleaned to remove organic compoundsdeposited on the wafer during the implantation process.

The front surface of the donor wafer is then bonded to a handle wafer toform a bonded wafer pair through a hydrophilic bonding process. Thedonor wafer and handle wafer are bonded together by exposing thesurfaces of the wafers to plasma containing, for example, oxygen ornitrogen. Exposure to the plasma modifies the structure of the surfacesin a process often referred to as surface activation. The wafers arethen pressed together and a bond is formed therebetween. This bond isrelatively weak, and must be strengthened before further processing canoccur.

In some processes, the hydrophilic bond between the donor wafer andhandle wafer (i.e., a bonded wafer) is strengthened by heating orannealing the bonded wafer pair at temperatures between approximately300° C. and 500° C. The elevated temperatures cause the formation ofcovalent bonds between the adjoining surfaces of the donor wafer and thehandle wafer, thus solidifying the bond between the donor wafer and thehandle wafer. Concurrently with the heating or annealing of the bondedwafer, the particles earlier implanted in the donor wafer weaken thecleave plane. A portion of the donor wafer is then separated (i.e.,cleaved) along the cleave plane from the bonded wafer pair to form theSOI wafer.

The bonded wafer is first placed in a fixture in which mechanical forceis applied perpendicular to the opposing sides of the bonded wafer inorder to pull a portion of the donor wafer apart from the bonded wafer.According to some methods, suction cups are utilized to apply themechanical force. The separation of the portion of the donor wafer isinitiated by applying a mechanical wedge at the edge of the bonded waferat the interface between the donor wafer and the handle wafer. Theapplication of the mechanical force initiates propagation of a cleavealong the cleave plane. The mechanical force applied by the suction cupsthen pulls a portion of the donor wafer away from the bonded wafer, thusforming an SOI wafer.

The resulting SOI wafer thus comprises a thin layer of silicon disposedatop the oxide layer and the handle wafer. The thickness of the layermay be non-uniform. The layer may also have a non-uniform roughness.This non-uniform thickness and roughness of the layer may be the resultof the cleave propagating at varying speeds and/or the mechanical forceapplied by the suction cups. Additional processing is thus required toreduce the variation in thickness of the layer and/or smooth this layer.These additional processing steps are both time consuming and costly.

Thus, there remains a continuing need for a system and method forcleaving a bonded wafer structure that results in the structure having alayer with a relatively uniform thickness and roughness.

This Background section is intended to introduce the reader to variousaspects of art that may be related to various aspects of the presentdisclosure, which are described and/or claimed below. This discussion isbelieved to be helpful in providing the reader with backgroundinformation to facilitate a better understanding of the various aspectsof the present disclosure. Accordingly, it should be understood thatthese statements are to be read in this light, and not as admissions ofprior art.

SUMMARY

One aspect of the present disclosure is directed to an apparatus forcleaving a bonded wafer structure that includes a first wafer and asecond wafer. The first wafer has a peripheral edge that includes afirst portion and the second wafer has a peripheral edge that includes asecond portion. The first portion is disposed opposite the secondportion. The apparatus has a first arm, a first clamp, a second arm anda second clamp. The first clamp is mounted on the first arm and has asurface for contacting the first portion of the peripheral edge of thefirst wafer. The second clamp is mounted on the second arm and has asurface for contacting the second portion of the peripheral edge of thesecond wafer.

Another aspect of the present disclosure is directed to a method ofcleaving a bonded wafer structure that includes a first wafer and asecond wafer. The first wafer has a peripheral edge that includes afirst portion and the second wafer has a peripheral edge that includes asecond portion. The first portion is disposed opposite the secondportion. The first portion of the peripheral edge of the first wafer iscontacted with a surface of a first clamp mounted on a first arm. Thesecond portion of the peripheral edge of the second wafer is contactedwith a surface of a second clamp mounted on a second arm. The bondedwafer structure is cleaved by at least one of (1) applying an upwardforce on the first wafer by actuating the first clamp upward or (2)applying a downward force on the second wafer by actuating the secondclamp downward.

A further aspect of the present disclosure is directed to an apparatusfor cleaving a bonded wafer structure that includes a first wafer and asecond wafer. The first wafer has a peripheral edge that includes afirst portion and the second wafer has a peripheral edge that includes asecond portion. The first portion is disposed opposite the secondportion. The apparatus includes a first grasping member and a secondgrasping member. The first grasping member has one or more annularmembers. The annular members have a surface for contacting the firstportion of the peripheral edge of the first wafer. The second graspingmember has one or more annular members. The annular members have asurface for contacting the second portion of the peripheral edge of thesecond wafer.

Yet another aspect of the present disclosure is directed to a method ofcleaving a bonded wafer structure that includes a first wafer and asecond wafer. The first wafer has a peripheral edge that includes afirst portion and the second wafer has a peripheral edge that includes asecond portion. The first portion is disposed opposite the secondportion. The first portion of the peripheral edge of the first wafer iscontacted with a surface of an annular member of a first graspingmember. The second portion of the peripheral edge of the second wafer iscontacted with a surface of an annular member of a second graspingmember. The bonded wafer structure is cleaved by at least one of (1)applying an upward force on the first wafer by actuating the firstgrasping member upward or (2) applying a downward force on the secondwafer by actuating the second grasping member downward.

Various refinements exist of the features noted in relation to theabove-mentioned aspects of the present disclosure. Further features mayalso be incorporated in the above-mentioned aspects of the presentdisclosure as well. These refinements and additional features may existindividually or in any combination. For instance, various featuresdiscussed below in relation to any of the illustrated embodiments of thepresent disclosure may be incorporated into any of the above-describedaspects of the present disclosure, alone or in any combination.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top view of an apparatus for cleaving a bonded waferstructure;

FIG. 2 is a perspective view of the apparatus of FIG. 1;

FIG. 3 is a cross-sectional view of FIG. 1 taken along the 3-3 lineshowing the apparatus prior to cleaving the bonded wafer structure;

FIG. 4 is a cross-sectional view of FIG. 1 taken along the 4-4 lineshowing the apparatus prior to cleaving the bonded wafer structure;

FIG. 5 is an enlarged portion of FIG. 3;

FIG. 6 is an enlarged portion of FIG. 4;

FIG. 7 is a perspective view of a clamp used in an apparatus forcleaving a bonded wafer structure;

FIG. 8 is a top view of an apparatus used for cleaving a bonded waferstructure before securing the structure;

FIG. 9 is a top view of an apparatus used for cleaving a bonded waferstructure after securing the structure;

FIG. 10 is a cross-sectional view of Figure taken along line 10-10;

FIG. 11 is a top view of an apparatus for cleaving a bonded wafer;

FIG. 12 is black and white ACCUMAP® image of a surface of a SOI waferafter cleaving by a conventional process using suction cups; and

FIG. 13 is black and white ACUMAP® image of a surface of a SOI waferafter cleaving by a process in which opposite forces are applied at thebonded wafer edge.

Corresponding reference characters indicate corresponding partsthroughout the drawings.

DETAILED DESCRIPTION

The embodiments described herein generally relate to apparatus andmethods for mechanically cleaving a bonded wafer structure such as abonded wafer pair. The apparatus and methods cleave (i.e., separate) thebonded structure along a cleave plane within the structure to form a newstructure such as a silicon-on-insulator (SOI) wafer. While reference ismade herein to use of the apparatus and methods to formsilicon-on-insulator structures, the systems and methods can also beused to form other structures without limitation.

FIGS. 1-7 depict an apparatus 100 for mechanically cleaving a bondedstructure 102. The bonded structure 102 shown in FIGS. 1-7 is a bondedwafer pair. However, it should be noted that structures other than abonded wafer pair may be cleaved by use of the apparatus 100. Referringto FIGS. 3 and 4, the structure 102 is separated along a cleave plane140 shown in phantom. The bonded structure 102 has an upper surface 106(generally, a first surface) and an opposing lower surface 108(generally, a second surface). The bonded structure contains a handlewafer 110 (generally, a first wafer) bonded to a donor wafer 112(generally, a second wafer) along a bond interface 104. The distancebetween the cleave plane 140 in the donor wafer 112 and the bondinterface 104 is exaggerated for the sake of clarity. Furthermore, inother embodiments, the position of the handle wafer 110 and the donorwafer 112 may be reversed such that the handle wafer is disposed beneaththe donor wafer.

As shown in FIGS. 5 and 6, the donor wafer 112 and handle wafer 110 arebeveled at their peripheral edge. It should be noted that the peripheraledge of the wafers may have a variety of geometries (e.g., rounded,bulleted). As used herein, the term “beveled” refers to a geometry inwhich the edge is not substantially perpendicular to the front and backsurface of the wafer and has one or more tapered edges and should not beconsidered in a limiting sense. Further, it should be noted that, asused herein a “tapered edge” refers merely to a surface at the waferedge that is not parallel to the front and back surfaces but ratherslopes upward or downward toward the portion of the edge that is mostdistant from the center of the wafer. Further, such “tapered edges” maybe straight or arcuate or may contain both straight and arcuateportions.

As also shown in FIGS. 5 and 6, the donor wafer 112 and handle wafer 110have rounded edges. The edge of the donor wafer 112 has a first portion148 and the edge of the handle wafer 110 has a second portion 152, thefirst portion being disposed opposite the second portion thereby forminga depression 144 between the two edges. Generally the first portion 148and second portion 152 are tapered edges of the wafer, the edges tapingupward or downward depending on the orientation of the bonded waferpair. As shown in FIGS. 5 and 6, the donor wafer 112 has a tapered edge146 (synonymously “upwardly tapered edge”) that slopes upward from thelower surface 108 of the bonded structure toward the portion (or “point”as with rounded edges) 154 of the edge that is most distant from thecenter of the wafer. The donor wafer 112 also includes an edge 148(synonymously “downwardly tapered edge” or “first portion” as describedabove) that slopes downward from the interface 104 toward the mostoutward portion 154 of the edge. Similar to the donor wafer 112, thehandle wafer 110 includes an upwardly tapered edge 152 (or “secondportion” as described above) that slopes toward the most outward portion156 of the edge of the handle wafer and a downwardly tapered edge 150that tapers to the most outward portion 156 of the edge of the handlewafer 110. The downward sloping edge 148 of the donor wafer 112 and theupward sloping edge 152 of the handle wafer 110 form a depression 144between the two edges.

As shown in FIGS. 1-4, the apparatus 100 includes a plurality of firstclamps 170 (or “upper clamps”) that releasably secure the handle wafer110 and a plurality of second clamps 184 that releasably secure thedonor wafer 112. The clamps 170, 184 are mounted respectively to firstarms 160 and second arms 166. The first arms 160 extend from a firstcentral disk 190 and the second arms 166 extend from a second centraldisk 192. The first central disk 190 may contact the upper surface 106of the bonded structure 102 to properly align the first clamps 170 inrelation to the structure 102. Similarly, the second central disk 192may assist in aligning the second clamps 184. The first clamps 170,first arms 160 and first central disk 190 together form a first graspingmember 120 (FIG. 1) and the second clamps 184, second arms 184 andsecond central disk 192 together form a second grasping member 122 (FIG.4).

As shown in FIG. 1, the first grasping member 120 has four arms 160 andfour clamps 170 and the second grasping member 122 also has four arms166 and four clamps 184. However, it should be noted that each member120, 122 of the apparatus 100 may have more or less arms and clampswithout limitation. In some embodiments, the apparatus 100 does not havearms but rather annular members for gripping the respective wafers asshown in FIGS. 8-10 and described below.

Each first clamp 170 has a surface 130 (FIGS. 3 and 5) which contactsthe upwardly tapered edge 152 of the handle wafer 110. Similarly, eachsecond clamp 184 has a surface 130 (FIGS. 4 and 6) that contacts thedownwardly tapered edge 148 of the donor wafer 112. As shown in furtherdetail in FIG. 7, the end portion of the first clamp 170 has a curvedprofile such that the surface 130 of the arm may enter the depression144 and contact the upwardly tapered edge 152 of the handle wafer 110(FIG. 5). In this regard, the term “curved” should not be consideredlimiting and refers to a profile in which the arm generally changes itsangular direction relative to other portions of the arm and may includeone or more discreet changes in direction (e.g., the arm may form one ormore angles within its length).

It should be noted that while the first clamp 170 is shown with acurvature of 180°, in other embodiments such as embodiments wherein thearm does not extend from the center of the bonded structure, the clampmay have a curvature other than 180°. For example, the arm 160 may beperpendicular to the front and back surfaces of the bonded structure andthe clamp 170 may curve about 90° into the depression 144 to contact itssurface 130 with the tapered edge 152. In some embodiments, the clamp170 does not have a curved profile such as embodiments wherein the armextends from the opposite direction as the arm shown in FIG. 7 (i.e.,from outside of the bonded structure). In this regard, the second clamp184 may have a shape and/or dimensions similar to the first clamp 170.However, the second clamp 184 is oriented opposite that of the firstclamp 170 to allow the second clamp 184 to grasp the donor wafer 112(i.e., the clamp 184 curves upward towards the depression 144 (FIG. 5)rather than downward). The clamps 170, 184 may have other shapes and/ordimensions (e.g., different from each other) without limitation.

As shown in FIG. 7, the first clamp 170 converges to form an edge whichis the surface 130 which contacts the handle wafer 110 of the bondedstructure 102. However, in other embodiments, the surface 130 may alsohave a width (i.e., the surface may be rectangular or square rather thanan edge) or may be a singular point which contacts the surface. Further,the surface 130 may be arcuate and optionally may have a shape which iscomplementary to the tapered edge of the handle wafer to increasecontact between the handle wafer and the surface 130. The surface 130 ofthe second clamp 184 may have a shape described above in regard to thesurface 130 of the first clamp 170.

To separate the bonded structure 102, the first grasping member 120and/or the second grasping member 122 grasps that bonded structure.Before being grasped, the bonded structure 102 may be moved intoposition by robotic means or by use of one of more of the graspingmembers 120, 122. Before cleaving, the other grasping member grasps thestructure. The bonded structure 102 may be grasped by the first graspingmember 120 by extending and retracting one or more of the arms 160 ofthe member 120 by use of a first actuator (not shown) that forms part ofor is attached to the first member 120. Similarly, the bonded structure102 is grasped by the second grasping member 122 by use of a secondactuator (not shown) that is attached to or forms part of the secondmember 122 to extend and retract one or more arms 166 of the secondgrasping member 122. Actuation of the arms 160, 166 of the firstgrasping member 120 and second grasping member 122 may be achieved byany method known to those of skill in the art including, for example,pneumatic, hydraulic or mechanical actuation.

After the bonded structure 102 is grasped by the first grasping member120 and the second grasping member 122, a force is applied to one orboth of the first grasping member 120 and second grasping member 122 toseparate the bonded structure 102 at the cleave plane 140. In thisregard, an actuator (not shown) may be attached to the first graspingmember 120. The actuator causes the first grasping member 120 to applyan upward force to the handle wafer 110 to separate the structure.Alternatively or additionally, an actuator (the same one or a differentactuator) may be attached to the second grasping member 122 that isoperable to cause the second grasping member 122 to apply a downwardforce on the donor wafer 112. The actuator(s) may be attached to theshafts 180, 182 or may be attached to other portions of the graspingmembers 120 or 122. It should be noted that only one of the firstgrasping member 120 and second grasping member 122 needs to be actuatedto provide the force used to separate the bonded structure and the otherclamp may be maintained in a stationary position. However, in someembodiments both the first grasping member 120 and second graspingmember 122 are actuated.

The cleaving process may be initiated by use of a blade (not shown) thatexerts force on the bonded structure 102. The blade is inserting intothe depression 144 formed between the handle wafer 110 and donor wafer112 and exerts force along the bonded structure edge. The force resultsin the initiation of a cleave along the cleave plane 140. This cleave incombination with the force exerted by one or both of the graspingmembers 120, 122 results in the cleaving and separation of the bondedstructure along the cleave plane 140. The blade is movable in a lateraldirection by an actuator (not shown) or other suitable mechanism.

In some embodiments of the present disclosure and as shown in FIGS.8-10, rather than having a plurality of arms, the grasping member mayinclude one or more annular members which at least partially encompassthe bonded structure. As shown in FIG. 8, the first grasping member 120includes a first annular member 194 and a second annular member 196 tograsp the handle wafer 110 of the bonded structure. The second graspingmember 122 (FIG. 10) may also have a first annular member 172 and asecond annular member 188 for grasping the donor wafer 112.

The first annular member 194 and second annular member 196 of the firstgrasping member 120 each have a surface 130 (FIG. 10) that contacts thefirst upwardly tapered edge of the handle wafer 110. Similarly, thefirst annular member 172 and second annular member 188 has a surface 130that contacts the downwardly tapered edge of the donor wafer 112. Asindicated by arrows in FIG. 8, the annular members 194, 196 are actuatedto contact the handle wafer 110 at its edge (FIG. 9). The annularmembers 172, 188 of the second grasping member 122 may be actuated in asimilar manner. Once the handle wafer and donor wafer are grasped, thefirst grasping member 120 and/or second grasping member 122 may beactuated to apply opposing forces and cause the bonded structure tocleave.

It should be noted that the annular members of the first grasping member120 and second grasping member 122 need not be arranged such that thehandle wafer 110 and donor wafer 112 are contacted continuously at theirrespective peripheral edges. The annular members may contact discreetportions of the peripheral edge (i.e., the annular members may have alength less than half the circumference of the bonded structure when thegrasping member has two annular members). Further, each grasping membermay have more than two grasping members without limitation.

In some embodiments, one or both of the grasping members are composed ofone annular member (i.e., the grasping member is a continuous annulus)that has an actuated edge that allows the grasping member to changediameter to allow the donor and/or handle wafer to be grasped andreleased after cleaving. An exemplary grasping member 120 is shown inFIG. 11. The grasping member 120 includes an actuated lip 176 which mayhave one or more actuated portions 108 which change the inner diameter Dof the grasping member upon actuation. The grasping member moves axiallywith respect to the bonded structure to grasp the bonded structure(i.e., approaches the bonded structure from above or below thestructure) rather than moving radially as with the grasping members 120,122 shown in FIGS. 8-10.

Without being held to any particular theory, it is believed thatnon-uniform thickness and/or roughness variations in the layers ofstructures (e.g., SOI structures) produced according to previous systemswere caused by localized stress applied to the surface of the bondedstructure. The embodiments described herein reduce or eliminate thisproblem by applying force at the wafer edge thereby reducing oreliminating thickness and/or roughness variations in the resultingdevice layer.

EXAMPLES

The processes of the present disclosure are further illustrated by thefollowing Examples. These Examples should not be viewed in a limitingsense.

Example 1 Comparison of the ACCUMAP® Image of a SOI Structure Cleaved byUse of Suction Cups and a SOI Structure Cleaved by Applying OpposingForces at the Wafer Edge

A bonded wafer pair was cleaved by a conventional process that usedsuction cups to separate the donor wafer from the resulting SOIstructure. The cleave was initiated by used of cleave blade. A secondSOI structure was also prepared by applying an upward and downward forceto the bonded structure after the cleave was initiated by the cleaveblade.

After the wafer was cleaved to produce the SOI structures, the surfaceof the device layer was imaged to produce an ACCUMAP® image (ACCUMAP®3220; ADE). The image produced from the SOI structure cleaved by theconventional method that used suction cups is shown in FIG. 12 and theimage produced from the SOI structure cleaved by applying oppositeforces at the bonded wafer edge is shown in FIG. 13. As can be seen fromFIG. 12, the SOI structure produced by using suction cups during thecleave had strong cleave striations at the bottom, far left and farright of the image. The SOI structure of FIG. 13 is more symmetrical andresults in greater thickness uniformity.

When introducing elements of the present disclosure or the embodiment(s)thereof, the articles “a”, “an”, “the” and “said” are intended to meanthat there are one or more of the elements. The terms “comprising,”“including,” “containing” and “having” are intended to be inclusive andmean that there may be additional elements other than the listedelements. The use of terms indicating a particular orientation (e.g.,“top”, “bottom”, “side”, etc.) is for convenience of description anddoes not require any particular orientation of the item described.

As various changes could be made in the above constructions and methodswithout departing from the scope of the disclosure, it is intended thatall matter contained in the above description and shown in theaccompanying drawing[s] shall be interpreted as illustrative and not ina limiting sense.

What is claimed is:
 1. A method of cleaving a bonded wafer structurecomprising a first wafer and a second wafer, the first wafer having aperipheral edge including a first portion, the second wafer having aperipheral edge including a second portion, the first portion disposedopposite the second portion, the method comprising: contacting the firstportion of the peripheral edge of the first wafer with a surface of anannular member of a first grasping member; contacting the second portionof the peripheral edge of the second wafer with a surface of an annularmember of a second grasping member, wherein the annular member of thefirst grasping member or the annular member of the second graspingmember has an actuated edge; actuating the actuated edge to grasp andrelease the first wafer or the second wafer; and cleaving the bondedwafer structure by at least one of (1) applying a force on the firstwafer by actuating the first grasping member or (2) applying a force onthe second wafer by actuating the second grasping member.
 2. The methodas set forth in claim 1 further comprising inserting a blade between thefirst wafer and the second wafer to initiate cleaving of the bondedwafer pair.
 3. The method as set forth in claim 1 comprising actuatingthe first grasping member to apply a force to the first wafer to cleavethe bonded wafer structure.
 4. The method as set forth in claim 3comprising actuating the second grasping member to apply a force to thesecond wafer to cleave the bonded wafer structure.
 5. The method as setforth in claim 1 wherein one or more annular members of the firstgrasping member continuously contact the first portion of the peripheraledge of the first wafer.
 6. The method as set forth in claim 5 whereinone or more annular members of the second grasping member continuouslycontact the second portion of the peripheral edge of the second wafer.7. The method as set forth in claim 1 wherein the first grasping membercomprises no more than one annular member.
 8. The method as set forth inclaim 7 wherein the second grasping member comprises no more than oneannular member.
 9. The method as set forth in claim 1 wherein the firstgrasping member comprises more than one annular member.
 10. The methodas set forth in claim 9 wherein the second grasping member comprisesmore than one annular member.